Objective To investigate the clinical features, diagnosis and treatment of mitochondrial cardiomyopathy. Methods We retrospectively analyzed a rare case of cardiomyopathy complicated with epilepsy caused by mitochondrial tRNA mutation and reviewed the related literature. Results A boy of 1 year and 3 months of age was admitted to hospital due to recurrent convulsions. The clinical manifestations were developmental retardation, left atrioventricular enlargement, myocardial hypertrophy, reduced left ventricular systolic function, increased blood lactic acid, and abnormal video electroencephalogram. Genetic testing found that the child carried an m. 4300 A>G mutation in tRNA gene, and he was diagnosed as mitochondrial cardiomyopathy. The metabolism is improved by using cardiotonic drug, diuretic drug, coenzyme Q10 and levocarnitine and antiepileptic drug treatment. At present, the patient was followed up for more than 3 months, his left atrium and ventricle was smaller than before, and the heart function was significantly improved. Conclusions The possibility of mitochondrial cardiomyopathy should be paid attention to when children’s cardiomyopathy is complicated with neurological dysfunction, hyperlactacidemia and other multi-system dysfunction.